Method for production of bone plates, in particular of plates for vertebral osteosynthesis

ABSTRACT

A method for producing bone plates includes the following steps: using a sheet ( 1 ) of titanium or of titanium alloy having a thickness of 1.7 to 2 mm; determining the direction of the fibres of this sheet ( 1 ) and cutting out portions ( 3 ) of sheet ( 1 ) parallel to the direction of the fibres of this sheet ( 1 ); cutting out, from each portion ( 3 ) of sheet, bone plates or bone plate blanks ( 4 ), in such a way that a longitudinal direction of these plates or blanks ( 4 ) is parallel to the direction of the fibres of the sheet ( 1 ); curving the sheets, plates or blanks in a suitable manner and then finishing the plates or blanks ( 4 ).

The present invention concerns a method for producing bone plates, inparticular plates for vertebral osteosynthesis.

It is common to use a plate made in titanium or titanium alloy in orderto maintain two vertebrae or more than two vertebrae in relation to eachother, this plate being placed against the vertebral bodies of thevertebrae and being secured to the latter parts using screws.

A plate of this type must have a shape curved in the transversedirection in order to adapt to the curvature of the vertebral bodies,and a shape curved in the longitudinal direction, enabling it to adaptto the lordosis of the vertebrae. It also comprises holes allowingpassage through it of its fastening screws, and can comprise slots,cut-outs, bores, openings, recesses or others.

The existing plates are, to date, systematically made from blocks orstrips cut out of laminated or forged sheets from titanium or titaniumalloy, having a thickness substantially larger than the thickness whicha finished plate must have, the aforementioned curvatures being formedby machining of the mass of this strip. For example, strips which havedimensions of 150 mm long by 35 mm wide and 7 mm thick, cut outtransversely in the sheets, are used to obtain a series of finishedplates with a thickness of 2.5 mm.

This production method is considered mandatory in order to obtain aplate able to resist the repeated stresses this plate undergoes afterimplantation. For the same reason, it is considered mandatory that sucha plate be approximately 2.5 mm thick.

The traditional method has the drawback of being long and costly toimplement, given the machining work to be done and the quantity ofmaterial lost.

Furthermore, this method has the drawback of creating “dead zones”, i.e.zones in which the integrity of the material is altered by theaggressive machining of a significant quantity of this material and bythe resulting heating. The resistance of the plates to fatigue isaffected by this, also making a thickness of the plates of at least 2.5mm necessary.

The aim of the present invention is to resolve all of these drawbacks.

Its main aim is therefore to provide a method for producing a boneplate, in particular a plate for vertebral osteosynthesis, which iseasier and less expensive to implement than the method according to theprior art, without decreasing the resistance of the obtained plate.

Another aim of the invention is to provide a method making it possibleto obtain plates having a more reduced thickness than the current plateswith equal resistance, in particular a thickness which can be from 1.7mm to 2 mm.

An additional aim of the invention is to provide a method which avoidsthe creation of “dead zones” in the obtained plate.

In order to achieve at least the main aim above, the method according tothe invention comprises the following steps:

-   a) using a sheet of titanium or of titanium alloy having a thickness    of 1.7 to 2 mm;-   b) determining the direction of the grain flow of this sheet;-   c) cutting out portions of sheet, parallel to the direction of the    grain flow of this sheet, sized so as to make it possible to obtain    a plurality of bone plates, these portions of sheet in particular    being in the form of strips;-   d) performing, in any order, operations d1, d2 and d3 below:-   d1) shaping the portions of sheet, or plates or blanks obtained by    operation d2, in particular by rolling or cold bending, in order to    form a curvature of the portions of sheet or of the plates or blanks    in the transverse direction and/or the longitudinal direction, in    order to obtain one or several curvatures suited to the shape of the    vertebrae and/or the lordosis of the vertebrae for which the plates    being manufactured are intended;-   d2) cutting out, in each portion of sheet, bone plates or bone plate    blanks, such that a longitudinal direction of these plates or blanks    is parallel to the direction of the grain flow of the sheet;-   d3) piercing and, if necessary, cutting out or machining portions of    sheet, or plates or blanks obtained by operation d2;-   e) finishing the plates or bone plate blanks.

The method according to the invention thus consists of determining the“grain flow” of the sheet, i.e. the orientation of the molecules of thematerial resulting from the lamination of the sheet, and cutting out thebone plates or the bone plate blanks such that the length of theseplates or blanks is parallel to the grain flow of the sheet, thesecutouts being done either before or after shaping of the strips orplates or blanks.

The applicant has indeed discovered that, in the traditional method, thegrain flow of the sheet is systematically oriented transversely to thelongitudinal direction of the bone plates obtained, the strips of sheetsin which these plates are cut out themselves having been cut outtransversely to the direction of the grain flow. This results in theunanimously accepted need, in order to obtain the appropriateresistance, to make bone plates whereof the curvatures are obtained bymachining and the minimal thickness of which is 2.5 mm.

On the contrary, the method according to the invention makes it possibleto obtain plates with the grain flow of the sheet oriented in thelongitudinal direction of the obtained plates, which allows the use ofsheets with a thickness limited to 1.7 to 2 mm and the shaping of theportions of sheet or of the blanks through relatively simple operations,in particular rolling or cold bending; the obtained bone plates have aresistance comparable to that of the 2.5 mm thick plates obtainedaccording to the prior art, and do not involve the implementation oflong and costly machining operations, which may also create alterationsin the integrity of the material (“dead zones”).

The determination of the grain flow of the sheet in step b) can be donethrough a macrographic analysis of the surface of this sheet.

The cut-outs of the portions of sheet or of the plates or blanks insteps c) and d2) can in particular be done using a pressurized water jetmachine, in particular of the numerical control type.

Water jet cutting is used rather than machining or laser cutting becauseit does not produce any cutting heat which would create particles ableto crumble and which would unfavorably change the structure of thefibers around the cut-out sector of the material.

The transverse curvature produced in step d1 can in particular begenerated by a radius of 80 mm and the longitudinal curvature can inparticular be generated by a radius of 300 to 400 mm.

Preferably, in step d2, the cutout blanks comprise protruding legsallowing them to be immobilized on a suitable machine in order toperform all or some of the operations of step d3) and step e); thefinishing operations of step e) then include the elimination of theseprotruding legs after performing the other finishing operations. Saidsuitable machine can in particular be a four- or five-axis shapingmachine (the three Cartesian axes and one or two axes of rotation).

According to another possible embodiment of the invention, the methodcomprises the following steps:

-   -   step a);    -   step b);    -   step c);    -   step d1): formation of the portions of sheet only in the        transverse direction;    -   step d2);    -   step d3);    -   step d4): shaping of the plates or blanks obtained in step d2)        in order to form a curve in the longitudinal direction, suitable        for the lordosis of the vertebrae for which the bone plates are        intended;    -   step e).

The operations of step d3) (piercing and others) and d4) (longitudinalcurvature) are therefore done on plates or bone plate blanks cut out instep d2).

According to another possible embodiment of the invention, the methodcomprises the following steps:

-   -   step a);    -   step b);    -   step c);    -   step d1): shaping of the portions of sheet in the transverse        direction and in the longitudinal direction;    -   step d3);    -   step d2);    -   step e).

The operations of step d1) (transverse and longitudinal curvatures) andd3) (piercings and others) are therefore done on the portions of sheetobtained in step c).

The method may comprise, after step d1 or d4, the performance of amacrographic analysis of the surface of at least one of the sides ofsaid portion of sheet, or of said plates or blanks.

This analysis makes it possible to ensure that no surface flaws orcracks were created during these steps d1) or d4).

The invention will be well understood, and other characteristics andadvantages thereof will appear, in reference to the appendeddiagrammatic drawing, illustrating, as non-limiting examples, portionsof sheet during two possible implementations of the method it concerns.

FIGS. 1 to 4 are very diagrammatic views of portions of sheet accordingto a first embodiment of the method, and

FIGS. 5 to 8 are very diagrammatic views of portions of sheet accordingto a second embodiment of the method.

For simplification, parts or elements which are found identically orsimilarly in both of these embodiments will be identified by the samenumerical references and will not be described again.

FIG. 1 illustrates a sheet 1 of titanium or of titanium alloy having athickness of 1.7 to 2 mm whereof the fibers, diagrammed by dotted lines2, are oriented in a determined direction (“grain flow”). This directionis that of the orientation of the molecules of the material resultingfrom the lamination of the sheet 1.

FIG. 2 shows a portion 3 of the sheet 1 dimensioned in order to allowobtaining of a plurality of bone plates, these bone plates beingvertebral osteosynthesis plates. The portion 3 of sheet has been cut outparallel to the direction of the fibers of the sheet 1; it can, forexample, be 160 mm long and 40 mm wide.

FIG. 3 shows blanks 4 of bone plates as they will be cut out in theportion 3 of sheet; they comprise a central part 4 a designed to formthe osteosynthesis plate strictly speaking and, at each longitudinal endof this central part, a protruding leg 4 b pierced by a hole. Theseprotruding legs 4 b allow the immobilization of the blanks 4 on asuitable machine for the performance of all or part of the piercingoperations, and if applicable the limited cutting and/or machiningoperations of the blanks 4, and finishing operations for the boneplates. These finishing operations in particular include the eliminationof the protruding legs 4 b.

It is essential to note that the blanks 4 are cut out such that thelongitudinal direction of these blanks is parallel to the grain flow ofthe portion 3 of sheet.

FIG. 4 shows that the portion 3 of sheet was curved transversely beforecutting out of the blanks 4, in particular by rolling or cold bending,such that these blanks 4 have, after cutting, a curvature suited to theshape of the vertebral bodies of the vertebrae for which they aredesigned to ensure mutual fastening. The radius generating thiscurvature can in particular be 80 mm.

The method corresponding to FIGS. 1 to 4 comprises the following steps:

-   -   step a): use a sheet 1 of titanium or titanium alloy having a        thickness of 1.7 to 2 mm;    -   step b): determine the grain flow of this sheet, through a        macrographic analysis of the surface of the sheet 1;    -   step c): cut out, using a pressurized water jet machine with        numerical controls, portions 3 of sheet 1, parallel to the grain        flow of this sheet 1;    -   step d1): shaping, by rolling or cold bending, portions 3 of        sheet 1 in the transverse direction, as shown in FIG. 4;    -   step d2): cutting out, using a pressurized water jet machine        with numerical controls, blanks 4 in each portion 3 of sheet 1,        such that a longitudinal direction of these blanks 4 is parallel        to the grain flow of the sheet 1;    -   step d3): placing blanks 4, using legs 4 b, in a shaping machine        with four or five axes (the three Cartesian axes and one or two        axes of rotation) then piercing, and if applicable, limited        cutting and/or machining, of the blanks 4;    -   step 4 d): shaping of the blanks 4 by rolling or cold bending in        order to grant them a curvature in the longitudinal direction        allowing them to be adapted to the anatomical lordosis of the        vertebrae for which the bone plates are intended; this curvature        is generated by a radius which can be from 300 to 400 mm;    -   step e): finishing operations for these plates and obtaining        bone plates by eliminating the legs 4 b.

FIGS. 5 to 7 correspond to FIGS. 2 to 4, respectively, showing a portion3 of sheet 1 as previously stated, which is curved, then in which theblanks 4 are cut out.

In this case, however:

-   -   the width of the portion 3 is smaller than that of the portion 3        of the preceding case, making it possible only to obtain a row        of blanks 4.    -   the portion 3 is bent longitudinally before cutting out the        blanks 4, as shown by FIG. 8.

The method corresponding to FIGS. 5 to 8 comprises the following steps:

-   -   step a) as previously stated;    -   step b) as previously stated;    -   step c) as previously stated;    -   step d1): shaping of the portions 3 of sheet in the transverse        direction and in the longitudinal direction;    -   step d3): placement of the portions 3 of sheet in a shaping        machine with four or five axes (the three Cartesian axes and one        or two axes of rotation) then piercing, and if applicable        limited cutting and/or machining at the appropriate locations;    -   step d2): removal of the portions 3 of sheet from said machine        and cutting out of the blanks 4 as previously stated;    -   step e) as previously stated.

The operations of step d1) (transverse and longitudinal curvatures) andd3) (piercings and others) are therefore done on the portions of sheetobtained in step c).

Either of the aforementioned implementations of the method can comprise,after step d1 or d4, the performance of a macrographic analysis of thesurface of at least one of the sides of the portion 3 of sheet, or ofsaid blanks 4 in order to ensure that no surface flaws or cracks werecreated during these steps d1) or d4).

The invention thus provides a method for producing bone plates, inparticular plates for vertebral osteosynthesis, having for determiningadvantages:

-   -   being easier and less costly to implement than the method        according to the prior art, without decreasing the resistance of        the obtained plate;    -   making it possible to obtain plates having a smaller thickness        than the current plates with equal resistance, in particular a        thickness which can be from 1.7 mm to 2 mm;    -   avoiding the creation of “dead zones” in the obtained plate.

It goes without saying that the invention is not limited to theembodiment described above as an example, but that it extends to allembodiments covered by the appended claims.

1. Method for producing bone plates, in particular plates for vertebralosteosynthesis, characterized in that it comprises the following steps:a) using a sheet (1) of titanium or of titanium alloy having a thicknessof 1.7 to 2 mm; b) determining the direction of the grain flow of thissheet (1); c) cutting out portions (3) of sheet (1), parallel to thedirection of the grain flow of this sheet (1), sized so as to make itpossible to obtain a plurality of bone plates, these portions (3) ofsheet in particular being in the form of strips; d) performing, in anyorder, operations d1, d2 and d3 below: d1) shaping the portions (3) ofsheet, or plates or blanks (4) obtained by operation d2, in particularby rolling or cold bending, in order to form a curvature of the portions(3) of sheet or of the plates or blanks (4) in the transverse directionand/or the longitudinal direction, in order to obtain one or severalcurvatures suited to the shape of the vertebrae and/or the lordosis ofthe vertebrae for which the plates being manufactured are intended; d2)cutting out, in each portion (3) of sheet, bone plates or bone plateblanks (4), such that a longitudinal direction of these plates or blanks(4) is parallel to the direction of the grain flow of the sheet; d3)piercing and, if necessary, cutting out or machining portions (3) ofsheet, or plates or blanks (4) obtained by operation d2; e) finishingthe plates or bone plate blanks (4).
 2. Method according to claim 1,characterized in that the determination of the grain flow of the sheet(1) in step b) is done through a macrographic analysis of the surface ofthis sheet (1).
 3. Method according to claim 1, characterized in thatthe cut-outs of the portions (3) of sheet or of the plates or blanks (4)in steps c) and d2) are done using a pressurized water jet machine, inparticular of the numerical control type.
 4. Method according to claim1, characterized in that the transverse curvature produced in step d1 isgenerated by a radius of 80 mm and the longitudinal curvature isgenerated by a radius of 300 to 400 mm.
 5. Method according to claim 1,characterized in that, in step d2, the cutout blanks (4) compriseprotruding legs (4 b) allowing them to be immobilized on a suitablemachine in order to perform all or some of the operations of step d3)and step e); the finishing operations of step e) then include theelimination of these protruding legs (4 b) after performing the otherfinishing operations.
 6. Method according to claim 5, characterized inthat said suitable machine is a four- or five-axis shaping machine (thethree Cartesian axes and one or two axes of rotation).
 7. Methodaccording to claim 1, characterized in that comprises the followingsteps: step a); step b); step c); step d1): formation of the portions(3) of sheet only in the transverse direction; step d2); step d3); stepd4): shaping of the plates or blanks (4) obtained in step d2) in orderto form a curve in the longitudinal direction, suitable for the lordosisof the vertebrae for which the bone plates are intended; step e). 8.Method according to claim 1, characterized in that comprises thefollowing steps: step a); step b); step c); step d1): shaping of theportions (3) of sheet in the transverse direction and in thelongitudinal direction; step d3); step d2); step e).
 9. Method accordingto claim 1, characterized in that it comprises, after step d1 or d4, theperformance of a macrographic analysis of the surface of at least one ofthe sides of said portion (3) of sheet, or of said plates or blanks (4).10. Method according to claim 2, characterized in that the cut-outs ofthe portions (3) of sheet or of the plates or blanks (4) in steps c) andd2) are done using a pressurized water jet machine, in particular of thenumerical control type.
 11. Method according to claim 2, characterizedin that the transverse curvature produced in step d1 is generated by aradius of 80 mm and the longitudinal curvature is generated by a radiusof 300 to 400 mm.
 12. Method according to claim 3, characterized in thatthe transverse curvature produced in step d1 is generated by a radius of80 mm and the longitudinal curvature is generated by a radius of 300 to400 mm.
 13. Method according to claim 2, characterized in that, in stepd2, the cutout blanks (4) comprise protruding legs (4 b) allowing themto be immobilized on a suitable machine in order to perform all or someof the operations of step d3) and step e); the finishing operations ofstep e) then include the elimination of these protruding legs (4 b)after performing the other finishing operations.
 14. Method according toclaim 3, characterized in that, in step d2, the cutout blanks (4)comprise protruding legs (4 b) allowing them to be immobilized on asuitable machine in order to perform all or some of the operations ofstep d3) and step e); the finishing operations of step e) then includethe elimination of these protruding legs (4 b) after performing theother finishing operations.
 15. Method according to claim 4,characterized in that, in step d2, the cutout blanks (4) compriseprotruding legs (4 b) allowing them to be immobilized on a suitablemachine in order to perform all or some of the operations of step d3)and step e); the finishing operations of step e) then include theelimination of these protruding legs (4 b) after performing the otherfinishing operations.
 16. Method according to claim 2, characterized inthat comprises the following steps: step a); step b); step c); step d1):formation of the portions (3) of sheet only in the transverse direction;step d2); step d3); step d4): shaping of the plates or blanks (4)obtained in step d2) in order to form a curve in the longitudinaldirection, suitable for the lordosis of the vertebrae for which the boneplates are intended; step e).
 17. Method according to claim 3,characterized in that comprises the following steps: step a); step b);step c); step d1): formation of the portions (3) of sheet only in thetransverse direction; step d2); step d3); step d4): shaping of theplates or blanks (4) obtained in step d2) in order to form a curve inthe longitudinal direction, suitable for the lordosis of the vertebraefor which the bone plates are intended; step e).
 18. Method according toclaim 4, characterized in that comprises the following steps: step a);step b); step c); step d1): formation of the portions (3) of sheet onlyin the transverse direction; step d2); step d3); step d4): shaping ofthe plates or blanks (4) obtained in step d2) in order to form a curvein the longitudinal direction, suitable for the lordosis of thevertebrae for which the bone plates are intended; step e).
 19. Methodaccording to claim 5, characterized in that comprises the followingsteps: step a); step b); step c); step d1): formation of the portions(3) of sheet only in the transverse direction; step d2); step d3); stepd4): shaping of the plates or blanks (4) obtained in step d2) in orderto form a curve in the longitudinal direction, suitable for the lordosisof the vertebrae for which the bone plates are intended; step e). 20.Method according to claim 6, characterized in that comprises thefollowing steps: step a); step b); step c); step d1): formation of theportions (3) of sheet only in the transverse direction; step d2); stepd3); step d4): shaping of the plates or blanks (4) obtained in step d2)in order to form a curve in the longitudinal direction, suitable for thelordosis of the vertebrae for which the bone plates are intended; stepe).